Wheel cylinder



WHEEL CYLINDER Original Filed Feb. lO, 1 942 f7 w ma@ @my Patented Feb.. 7, 1950 UNITED STATES OFFICE Original application February 10, 1942, Serial No. 430,296, now Patent No. 2,444,181, dated June 29, 1948. Divided and this application July 24,

1947, Serial No. 763,368.

9 Claims.

l This application is a division of application Serial No. 430,296, iiled February 10, 1942, now Patent No. 2,444,181, granted June 29, 1948, Which was a, continuation in part of application S. N. 143,805, now Patent No. 2,276,009, granted March 10,1942.

This invention relates to improvements in wheel cylinders and more particularly to the arrangement and structure of the pistons and piston packings for the Wheel cylinders.

An object of this invention is to provide a piston in which elastic packing rings are freely mounted between rigid piston members which are co-axial with the rings and are held together as a unit under yielding counteracting mechanical axial pressure.

Another object is to simplify the construction of the pistons to lower production costs and ensure maximum unication of the Working parts.

Still another object is to provide packings for the pistons which are readily adaptable to relatively high temperatures Without unduly increasing the frictional resistance to reciprocal movements in the cylinders.

Other objects and advantages of the invention will appear during the course of the following description.

These improvements may be put into practice in various Ways, and in the accompanying drawing is illustrated by Way of example a form of practical application of the invention to a wheel motor cylinder.

Fig. 1 is a longitudinal sectional View of a Wheel cylinder with opposed pistons constructed according to the present invention. i

Fig. 2 is an enlarged longitudinal sectional view of the packing element of Fig. 1 showing thermic deformation of the element.

As illustrated in Fig. l tWo opposed pistons A and B, each comprising elements 4, 5, 6 are mounted in a motor cylinder i as commonly located between the brake shoes in the wheels of motor vehicles, and is suitably connected with the master cylinder. They are held in spaced relation to each other at the centre of the cylinder I under counteracting pressure of the compensator spring I4 and the brake shoes return spring I5. The spacing of the opposed pistons at the centre of the cylinder may be secured by a cam registering device c commonly mounted against the inner rims of the brake shoes.

The counteracting mechanical pressure under which the opposed pistons A and B are mounted in the cylinder is suicient toexpand the packing rings 5 radially into permanent partial static con- In Italy March 24,

tact with the cylinder Wall at the apex of their elastic peripheries to ensure an initial hydraulic seal regardless of the thermal deformation of the rings. The iluid pressure takes effect on the piston assemblies 1, 5, 6, moving them in opposite directions and simultaneously expanding the packing rings into an effective dynamic seal against the cylinder Wall. Upon release of pressure, the rings contract and the piston assemblies return to their starting positions under the urging of spring I5. In fact under the influence of braking heat which in the wheel cylinders may reach a temperature of degrees centigrade or more, the elastic mass expands to a considerable extent and when packings are used which have a maximum free diameter equal to that of the cylinder bore, the radial thermal expansion will be rigidly resisted by the cylinder Wall and an axial flow of the elastic mass will result. This flow produces a permanent deformation of the packings which, as indicated by the dotted lines on Fig. 2 will as sume a free diameter at the apex of the periphery which is less than the diameter of the cylinder bore with a corresponding contraction in the elastic bore and an increase in the length. After this intial thermal deformation has taken place, the shape of the packings remains unchanged in subsequent heatings of like temperature and the counteracting radial and axial hydraulic pressure on the elastic bodies tends to keep it so, as already described.

As already indicated, the counteracting press ure of the compensator spring I4 and the brake shoes return spring I5 on the elastic packing, rings tends to keep them in permanent partial static contact with the cylinder wall under all circumstances and thus provide a positive seal against escape of fluid and influx of air. Any radial thermal contraction of the rings is automatically taken up by the counteracting axial pressure of springs I4 which holds the freely mounted piston parts in engagement with one another and permits of their free return as a unit in the cylinder upon release of pressure, under action of the return spring. By keeping the mean free external diameter of the packing rings well under that of the cylinder bore, a piston with Very low frictional resistance is secured even when subjected to heat and this ensures a prompt return of the pistons under release of the hydraulic pressure with consequent ready recovery of the brake shoes.

Owing to the structure of the elastic packing rings which have suilicient body to support of themselves the axial mechanical compression without buckling or twisting in the cylinder, rigid supports within the elastic bodies may be dispensed with and the rings may be freely mounted between their rigid terminals 4 and 6 as illustrated. This is important because such supports aggravate the thermaldeformation by rigidly resisting theA inner radial: expansion. ofl

the rings and increasing the axial iiow of the elastic mass which also increases the frictional.

resistance of the packings in the cylinder under heat. It might be noted in passing,` moreover, that thermal deformation. of the p ackings may be prevented altogether by f'asliioningv them with a free maximumv external diameter:

which is less than that oft thecylinder.v bore;

the diierence in diameter being equaltoV orflessithan the factor of the thermal expansiorr of the packings. The axial compression of the compensator spring l', however, must always be suicient initially to expand the rings radially into partial static. contact. with .the cylinder. wall,V

asl already described.

It .is understood v thatthe. various constructions and arrangements ofthe parts as. illustrated and described are submitted asv practical embodiments of the working principles involvedand may bemodied' as to detailswithout departing from the spirit of the invention as defined'v by the appended claims..

What VI claim. is:

l. An hydraulic motor cylinderiand a piston movable therein,.an elastic sealing ring' for the piston anda thrust memberv for. the ring. me.- chanical means for supporting saidring between the. piston and thrust member, the. ringhaying amean external diameter which is less than the diameter ofthe cylinder borethe ring., being freely mounted and yieldably supported between the piston andthe thrust member by axial me.- chanical pressure andbeingunattached' to the said piston and thrust member, the ring being` subjected. to axial. andV radial l hydraulic pressure.

and. being free to. expandand contract during,

its reciprocalmovements inthe cylinder with the piston and thrust members..

2. An hydraulic motor cylinder, a piston afseal ing ring and a thrust'. member. slidable.. in the,

cylinder, means for. yieldably supporting said ring between said piston. and thrust.. member,

the ring being freely mounted 'and .yieldably supported between adjacent faces ofthepistonand thrust .member under. axial .mechanicalpressura and being unattachedf4 to. the pistonand'thrust.

member, theringbeing initially, andnormally in partial contactwith the; cylinderiwall and bef ing subjected to. axial and radial. hydraulic pressure, saidpressurecausing. the ring to expand and contract initsreciprocal movements Vinthe cylinder with the piston and thrust member.

3. Amotor cylinder, a pistorrmoyable therein, an elastic sealing ring for said piston having an annular inner and outerv surface and two. end

faces, and a thrust memberhaving ,an axialbore extending therethrough, means for yieldably supporting said ring between said piston. and thrust member, the ring being freely mounted and yieldably supported by axially appliedmechanical pressure between adjacent faces. of the. pis

ton and thrust member, and'being. unattached, thereto, the saidpiston, ring andthrust mem f ber.. being free to.. slideY as. a .unit in the. cylinder, the annular outer surface of the ring being nor..- mally and initiallypartially spaced ,from the cylinder. wall andbeing. freeto expandand contract under axial. and. radial `hydraulic pressure,

the said radial pressure taking effect through the thrust member bore on the inner annular surface of the ring and the said axial pressure on the end faces of same.

4. An hydraulic motor cylinder, a pair of pistons for.. the cylinder, anelasticsealing ring for each pistonwitha maximum meanexternal diameter which is less than the diameter of the cylinder bore, and a thrust member for each ring mechanical means within and outside of the cylinder for urging the pistons, rings and thrust members. in opposite directions, each ring being freely mountedand yieldably supported between two adjacent-faceszof-,the piston and thrust mems ben'underfcounteracting axial mechanical pressure, being unattached to same and being free to=s1ideV inthey cylinder as a unit with the piston and thrust member, one of the counteracting axial mechanical pressure means bearing on the thrust member and the other counteracting axial mechanical pressure means bearing on the. piston, thering` being'.free to' expand"` and contract under axial and radial hydraulicpressure in its slid'able movements in the cylinder.

5. An hydraulicmoton cylinder appistonlmovable therein and" stop means limiting the retractile movement of the piston inthe cylinder, an elasticsealingfring'for'the piston having two endifaces and outer andirmer annul'ansurfaces, and a thrust` member foi" the` ring" havingV an axial. bore therethrough', the said piston ring and thrust memberbeing vslidablein the cylinder unit, the ring being" fi'eely" mounted and yieldably supported' between they piston and" thrust memberandiunattaclied to same 'means for subjecting" saidv ring` to' counteracting" mechanical forces against said end faces,.respectively, said ring,f having its outer' annular. surface initially and statically in partial contact witnthe cyl'- inder wall and being" free to expand. andlcontract' in the*v cylinder under'counteracting axial and radial hydraulic" pressure, the said radial pressure being applied to` the inner annular. surface of the ring'tlirough the axial bore ofthe thrust member and the said"axial pressure being applied bymeansy of'ithe thrustm'e'mber on the axial faces of the ring;-

6. An hydraulic brake wheel motor comprisingaicylinderanda piston operable'therein, the.

piston' including ahead; a thrustmember, and an expansible packingbetween saidV head'and thrust member, said' packing" being" physically unattached to said head. or thrust member and being" freely supported and s'elfcenteringr in the cylinder under the pressures developed therein, and being expansible'.. into sealing contact with the cylinder wall to eii'ecia'l fluid seal upon thev application of lhydraulic Ypressure thereto.

7. Awheel motor for ahydiaulic brake. system comprising a cylinder open. at". its ends, a pair of oppositely disposed pistons movable in said cylinder, ksaid .l pistons eachhaving anexpansible packing, mechanical means forexpanding said packings into static contact "withthefcylinder wall to prevent the. escape of. hydraulic fluid within the systemsaid/ packings-:being further.

expanded'into dynamicrandfpressuresealing con-4 tact withthe said cylinder walll on. the appli.

pistons. each.r having, an expansiblepacking, mev chanical means for expandingsaid packings yinto static Contact withtheicylindenwall -to prevent the escape cf hydraulic uid within the system, said packings being furtherwexpanded into dynamic and pressure sealing contact With said cylinder Wall on the application of Working presu sure to said motor. n

9. A Wheel motor for a hydraulic brake system comprising a cylinder, a pair of oppositely disposed pistons movable in the cylinder, an inlet in the cylinder for introducing fluid under pressure thereto between said pistons, each piston including an expansible packing movable with said piston but not physically attached thereto, being freely supported and self centering in the cylinder, mechanical means between said packings tending to -expand them into light static contact with the cylinder Wall to prevent escape PHILIP SIDNEY BALDWIN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Name Date Baldwin Aug. 10, 1943 Number 

